JPH0229990B2 - GASURYUSOKUSOKUTEIHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for measuring the flow rate of gas such as gas in a blast furnace, which is at high temperature and contains a large amount of dust.
More specifically, the present invention relates to a gas flow rate measurement method that measures the flow rate from the amount of convective heat transfer from a heating body placed in a fluid to be measured.

[Prior art]

Conventionally, differential pressure methods such as pitot tubes and hot wire anemometers have been used to measure the flow velocity of fluids, but with these methods, it is difficult to measure the flow rate of fluids when measuring high-temperature fluids that contain a large amount of dust. Measurements were difficult due to clogging and damage to the heating wire.

On the other hand, JP-A-57-106867, JP-A-53-
No. 54072, JP-A-54-118881, etc., a heating element with sufficient mechanical strength is inserted into the fluid to be measured as a probe, and the temperature of the heating element is set to a certain temperature difference with respect to the gas temperature. A method has been proposed in which the amount of heat dissipated from the heating element is controlled and the flow velocity is determined by measuring the cooling rate of the heating element or the power supplied to the heating element.

However, these methods have a problem in that when the temperature of the measured gas exceeds 400° C., the amount of radiant heat transferred from the probe increases as shown in FIG. 11, resulting in a large error. That is, the amount of heat transfer that is related to the flow rate is the amount of convective transfer, and an increase in the amount of radiant heat transfer that is not related to the flow rate results in a measurement error.

In fact, assuming that the heating body is a cylinder with a diameter D and a length L, the convective heat transfer flux Q _c is expressed by equation (1).

Q _c = hA (T _s − T _g ) ...(1) where, T _s = surface temperature, T _g = gas temperature h = k/Df (Re, Pr) convective heat transfer coefficient k = film thermal conductivity , R _e = Reynolds number, P _r = Prandtl number, A = heat transfer area The specific form of h is, for example, for 0.1<R _e <10 ³ h = k/D (0.35 + 0.47R _e ^0.52 ) P _r ^0.3 (Chemical Engineering Handbook P279) Also, the radiation heat transfer flux is expressed by equation (2).

Q _r σAFε(T _s ⁴ −T _g ⁴ ) ……(2) However, σ = Stephan-Boltzmann constant F = View factor ε = Emissivity Here, D = 5〓, L = 20 mm, T _s − T _g = 100°C, Q _r /Q _c 2 to 2.5 (T _g = 600°C, V = 4 m/S). Therefore, in order to measure the wind speed of high-temperature fluids of 400°C or higher, it is necessary to reduce this radiation heat transfer error.

On the other hand, as a method to eliminate the radiation heat transfer effect,
−66477 is proposed. This method measures the amount of heat supplied Q _a , Q _b and the surface temperature T _a , T _b of the heating body in order to control the heating body in the fluid to be measured at two different temperatures T _a , T _b . The purpose is to calculate the transfer coefficient α _c using equation (3).

α _c =σεT _a ⁴ −T _b ⁴ /T _a −T _b K ₁ +1/AQ _a −Q _b /T _a −T
_b K ₂ ...(3) The disadvantages of this method include the following points.

Two temperatures T _a and T _b are set for one measurement, and each data Q _a , Q _b , T _a , T _b is calculated from the thermal equilibrium state.
needs to be measured, which increases the measurement time.

It is necessary to accurately measure the absolute values T _a and T _b of the surface temperature of the heating element, but it is practically difficult to accurately measure the surface temperature of the heating element without being affected by radiant heat transfer at high temperatures. . Although it is necessary to use thin thermocouples to minimize radiation effects,
In this case, a problem arises in durability.

In equation (3), emissivity ε is difficult to evaluate accurately.
are directly included, and the method for evaluating the correction coefficients K ₁ and K ₂ is not clear.

[Purpose of the invention]

The present invention was made in view of the problems and shortcomings of the prior art, and its purpose is to reduce the amount of radiant heat transfer and to reduce the temperature of the gas to be measured by 400°C.
The aim is to realize a method that can accurately measure flow velocity even at temperatures as high as 0.degree. C. or higher.

[Summary of the invention]

The method of the present invention for achieving such objects includes: a heating probe having a built-in heater and a first temperature sensor; a heating probe having a built-in heater and a second temperature sensor; Target 2
An outer radiation shield body surrounded by a heavy structure,
A signal from the first temperature sensor and a signal from the second temperature sensor are input to control the amount of power given to each heating element so that the temperature of the outer radiation shield body becomes equal to the temperature of the inner heating element probe. The structure is characterized by the fact that it is equipped with a control means.

[Embodiments of the invention]

FIG. 1 is a configuration explanatory diagram for explaining an embodiment of the present invention. In the figure, reference numeral 1 denotes a heating probe in which a heater 11 and a first temperature sensor 12 are built. Reference numeral 2 denotes an outer radiation shield body installed so as to partially surround the heating body probe 1 so as to have a double structure, and a heater 21 and a second temperature sensor 22 are housed in this outer radiation shield body. 3 inputs the signal from the first temperature sensor 12 and the signal from the second temperature sensor 22, and calculates the temperature (t ₂ ) of the radiation shield body 2 and the temperature (t 1 ) of the heating body probe _1. ), 4 is the heating and cooling characteristics of the probe (e.g. cooling time constant).
This is a calculation indicator that determines the flow velocity of the gas to be measured and indicates it.

In the method according to the present invention, the surface temperature (t ₂ ) of the outer radiation shield body 2 is determined by the inner heating element probe 1
The temperature is controlled to be the same as the surface temperature (t ₁ ) of the inner heating element probe 1, thereby reducing the amount of radiant heat transfer from the inner heating element probe 1 and keeping the measurement error due to radiant heat transfer within the desired error. It has characteristics. This point will be explained below.

Radiation heat transfer flux Q _r,w of double structure probe
is expressed by Equation (4) based on the concept of Hottel's direct exchange area, which takes reflection into account, with reference to Figure 1.

Q _r,w = ₁₂ 〓(T ₁ ⁴ −T ₂ ⁴ ) + ₁₃ 〓(T ₁ ⁴ −T _g ⁴ ...(4) Therefore, if T ₁ = T ₂ , equation (4) becomes ( 5) The formula is as follows.

Q _r,w = ₁₃ 〓 (T ₁ ⁴ − T _g ⁴ ) ...(5) Here, ₁₃ = F (F ₁₂ , F ₁₃ , F ₂₃ , ε ₁ , ε ₂ , A ₁ , A ₂ ) F _ij = View factor of surfaces i, j ε _i = Emissivity of surface i A _i = Heat transfer area of surface i T ₁ = Probe temperature T _g = Gas temperature Q _r,w = Radiation heat transfer with shield Flux Now, in Figure 1, the outer radiation shield body 2
By reducing the opening area of the opening 20 through which the gas to be measured flows in and out, the view factor can be reduced.
F ₁₃ and F ₂₃ become small, and the radiation heat transfer flux can be made negligibly small compared to the convective heat transfer flux Q _c . In this case, it is sufficient to make the surface temperatures T ₁ and T ₂ equal, and it is not necessarily necessary to measure the absolute value of the surface temperatures.

FIG. 2 is a perspective view showing an example of the configuration of essential parts of an apparatus for carrying out the present invention, and FIG. 3 is a sectional view thereof. In this embodiment, the inner heating body probe 1 and the outer shield body 2 are both wound with wire heating bodies having the same wire diameter d, and the winding diameters are 2·R ₁ and 2·R _{2 ,} respectively. , with a winding length of H, fixedly installed in a concentric cylindrical shape. Further, a radiation shield cylinder 5 without temperature control is further installed outside the outer shield body 2. This radiation shield cylinder 5 serves to reduce the amount of radiation heat transfer to the outer shield body 2 as much as possible.

FIG. 4 is a side view of the linear heating body that constitutes the inner heating element probe 1 and the outer shield body 2 in FIG. 2, and FIG. 5 is a sectional view thereof.
This linear heating body incorporates a sheath heater 61 and a sheath thermocouple 62 as a temperature sensor, and has a sheath structure in which MgO is filled around these to ensure durability. Note that the temperature contact point (temperature measurement part) 63 of the thermocouple 62 is located near the center in consideration of symmetry and the like.

Inner heating probe 1 and outer radiation shield body 2
If both of these are constructed using a linear heating body having such a structure, the following advantages will occur.

The time constants of the inner probe 1 and the outer shield body 2 can be made equal regardless of the winding diameter, and by slightly changing the length H, the time constant of the outer shield body 2 can be made somewhat smaller than that of the inner probe 1. It is. By setting in this way, the temperature control of the outer shield body 2 can be made to follow the temperature of the inner probe 1 only by heating.

By flowing a constant current, the internal temperature distributions of the inner probe 1 and the outer shield body 2 can be made the same, and the surface temperature T _s can be accurately controlled by the internal temperature.

In the structure shown in FIGS. 2 and 3, the temperature (t ₂ ) of the outer shield body 2 is determined by the inner heating element probe 1.
If the temperature is controlled to _be equal to the temperature (t ₁ ) of
It can be expressed by a formula.

Q _r,w = _1g (F ₁₁ , F ₁₄ , F ₂₃ , F ₂₅ , F ₃₃ , F ₃₅ , ε, ε _s , A ₁ , A ₁ ′, A ₂ ) σ(T ⁴ −T _g ⁴ ) … …(6) On the other hand, the amount of radiant heat transfer Q _r,w/p when there is no shield
becomes equation (7).

Q _r,w/p = _1g (F ₁₁ , F ₁₄ , A ₁ , A ₁ ′, A ₂ , ε) σ (T ⁴ −T _g ⁴ ) ……(7) Here, the view factor F _ij is A _i F _ij = A _i F _ji , 〓 ⁱ F _ij =
1 (closed space), and the parameters R ₂ /R ₁ ,
It is a function of H/R ₁ and can be determined by calculation.

Here, when Q _r,w and Q _r,w/p are specifically determined, they are as shown in equations (8) and (9).

Q _r,w =A ₂ ε{F ₂₅ [1−(1−ε _s )F ₃₃ ]+(1
−ε _s )F ₂₃・F ₃₅ /1−(1−ε _s )F ₃₃ −(1−ε)(
1−ε _s )F ₃₂・F ₂₃ +2A′ ₁ /A ₂ +(A ₁ /A ₂ )F ₁₄ /1−(1−ε)
F ₁₁ }σ(T ⁴ −T _g ⁴ )……(8) Q _r,w/p =A ₂ ε{1+2A′ ₁ /A ₂ +(A ₁ /A ₂ )F ₁₄ /
1−(1−(1−ε)F ₁₁ }σ(T ⁴ −T _g ⁴ )……(9) Here, F ₁₄ =A ₄ /A ₁ {√ ² −4−(X−2)} F ₁₁ =1+(A ₄ /A ₁ ) {√ ₂ −4−(X−2)} X=2+H/R ₁ −d F ₃₂ =1/R−1/πR {cos ⁻¹ (B/A) -1/2L [
√(+2) ² −(2) ²・cos ^-1 (B/RA+Bsin ^-1 (1
/R−πA/2〕} F ₃₅ = 1-F ₃₂ -F ₃₃ F ₂₃ = (A ₃ /A ₂ )F ₃₂ F ₂₅ = 1-F ₂₃ R≡R ₂ /R ₁ , L≡H/R ₁ , A = L ² +R ² −1, B=L ² −R ² +1.

Figure 6 shows the parameters R≡R ₂ /R ₁ and L≡
It is a diagram showing the radiation heat transfer reduction effect (Q _r,w /Q _r,w/p ) for H/R ₁ . Here, both emissivity ε _s
= ε0.5, and it can be seen that the amount of radiant heat transfer can be reduced by 20% to 50% compared to the double shield type.

FIG. 7 is a diagram showing the ratio of radiant heat transfer flux and convective heat transfer flux in the double shield type. Here, for example, if the gas temperature is 600℃, R≡
If you set R ₂ /R ₁ = 1.5, L = H / R ₁ = 6,
It can be seen that Q _r,w /Q _c can be reduced to 10% or less. Also, regarding the emissivity, the emissivity of the inner probe ε
It can be said that the smaller is the radiation shielding effect, and the larger the emissivity ε _s of the outer radiation shield is, the greater the radiation shielding effect is.

FIG. 8 is an electrical connection diagram for measuring wind speed according to the present invention. The controller 3 includes a current control circuit 31, a changeover switch S _p and
It consists of a slider 32 connected to a 100V power supply. The calculation instruction circuit 4 also outputs a signal related to the temperature of the gas to be measured (T _g ), a signal related to the temperature of the heating element probe 1 (T ₁ ), and a signal related to the temperature of the outer radiation shield 2 (T ₂ ). It is comprised of a bias circuit 41 that inputs the signals from the bias circuit 41, and a recorder 42 that inputs each signal from the bias circuit 41, performs a predetermined calculation, and records it.

In this connection diagram, first select the selector switch S _p
is connected to the contact a side, and the temperature of the inner heating body probe 1 and the temperature of the outer radiation shield body 2 are both heated to a certain temperature higher than the temperature (T _g ) of the gas to be measured. Then, the predetermined temperature (T _n = T _g + ΔT)
When the _temperature reaches the temperature of
Temperature control is performed to follow the temperature of

FIG. 9 is a diagram showing the heating and cooling curves of the probe in the method of the present invention. Note that in this figure, time (t) passes from the right side to the left side as shown by the arrow. In this example, the flow velocity is determined by measuring the time constant of the cooling process of the probe, and a CA thermocouple is used as the temperature sensor.
CA thermocouple output V is ±1 in the range of 0℃ to 1000℃
It has a linear relationship with temperature with an accuracy of %, and therefore, if radiation heat transfer is ignored, it can be expressed by equation (10).

V=V _g + (V _n −V _g ) _e ^-t/ 〓 ……(10) 1/τ=A/HMeh, h=f(v) However, τ=time constant (sec)V _n =maximum heating Output (mV) V _g = gas temperature output (mV), HMe = probe equivalent heat capacity (kcal/℃), t = time (sec) Therefore, if the relationship between the cooling time constant τ and the flow velocity v is calibrated in advance, , τ can be measured to determine the flow velocity v.

As is clear from the diagram in FIG. 9, the temperature (t ₂ ) of the outer radiation shield body 2 changes during the cooling process.
Inner heating element probe 1 even without temperature control
The cooling characteristics are almost the same as the temperature (t ₁ ), but the effect of reducing radiant heat transfer is improved by controlling the temperature.

Note that in this example, the flow velocity v is determined by measuring the cooling time constant, but if the temperature of the probe is
Measure the power supply to keep the flow rate at V _nax .
You may also ask for

FIG. 11 is a diagram showing the relationship between the flow velocity v and the time constant τ in a conventional device using a single probe (D=5〓, 20 mm length cylindrical probe). When the gas temperature exceeds 400℃, the cooling effect due to radiant heat transfer becomes noticeable and the error increases.

FIG. 10 shows an apparatus according to the present invention (with the structure shown in FIG. 2, linear type 3.2%, inner heating body probe 1).
Winding diameter 2R ₁ = 16.4〓, outer shield winding diameter 2R ₂ =
24〓, winding length H = 35.2 mm, radiation shield cylinder inner diameter 50〓, wall thickness 2 mm) is a diagram showing the relationship between flow velocity v and time constant τ. As is clear from this diagram, in the apparatus of the present invention, the relationship between the flow velocity v and the time constant τ is suppressed to fluctuations of 10% or less between 200 and 600°C.

In the above embodiment, if the emissivity ε _s of the outer radiation shield body 2 is increased by applying a special paint or the like, the radiation heat transfer reduction rate can be further improved.

〔Effect of the invention〕

As explained above, according to the present invention, the amount of radiant heat transfer can be reduced, and the temperature of the gas to be measured can be reduced.
It is possible to realize a gas flow velocity measurement method that can accurately measure flow velocity even at high temperatures of 400° C. or higher.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing an example of an apparatus for carrying out the method of the present invention, FIG. 2 is a perspective view of its main part (probe), FIG. 3 is a longitudinal sectional view thereof, and FIG. FIG. 2 is a side view of the linear heating body constituting the heating body probe 1 and the outer shield body 2, FIG. 5 is a cross-sectional view thereof, and FIG. Figure 7 is a line diagram showing the ratio of radiant heat transfer flux and convective heat transfer flux in the present invention, Figure 8 is an electrical connection diagram for wind speed measurement, and Figure 9 is a line diagram showing the heating and cooling curves of the probe. 10 is a diagram showing the characteristics according to the method of the present invention, and FIG. 11 is a diagram showing the characteristics according to the conventional method. 1... Heating body probe, 11, 21... Heating heater, 2... Outer radiation shield body, 12, 22...
...Temperature sensor, 3... Control means, 4...
...Arithmetic indicator.

Claims (1)

[Claims] 1 A heating element probe with a built-in heater and a first temperature sensor; a heating element probe with a built-in heating heater and a second temperature sensor, with the heating element probe inside, and the heating element probe partially double-layered; and an outer radiation shield body surrounding the outer radiation shield body so that the temperature of the outer radiation shield body is measured by inputting a signal from the first temperature sensor and a signal from the second temperature sensor. A gas flow rate measuring method characterized by controlling the amount of electric power given to each heater so that the temperature is equal to the temperature of a heating element probe.